The present invention relates to a fluidized bed reactor. The fluidized bed reactor is in the upper part of a reactor chamber of which there is an outlet connected to a vortex chamber of a cyclone separator by means of a pipe tangentially connected thereto for separating solids conveyed by the gases being discharged from the fluidized bed reactor, and which comprises a return pipe for the separated solids, this pipe being connected to the lower part of the separator, and a gas discharge pipe disposed in the separator.
Fast fluidized bed technique utilizing solids circulation has been applied for a long time e.g. in roasting processes and nowadays more widely in various kinds of reactors, such as combustion chambers and gasifiers. In known applications, the separation of solids from the gases occurs in a conventional cyclone separator having a hopper-shaped lower part. The separator has a cylindrical vortex chamber in which there is disposed a gas discharge pipe conveying gases upwards and from which the solids are returned to the reactor through a gas lock. The duty of the gas lock is to prevent the reactor gases from flowing to the cyclone through the discharge pipe. Usually a mechanical locking device or in more developed equipment sand hovering in a U-tube acts as a gas lock of this kind. Especially in high-temperature-reactors the system for returning the solids is complicated expensive. The fact that part of the air required for fluidization in and the gas lock flows upwardly in the discharge pipe has a disadvantageous effect especially on the separation of light and fine-grained material. Moreover, a rising gas flow decreases the transport capacity of the discharge pipe.
It is known that a very low pressure and a high axial flow velocity are formed in the center of a conventional cyclone. Due to this, a conventional cyclone tends to suck from the stand pipe. The suction flow formed does not usually have a tangential velocity, so almost all the solids entrained by it are discharged through the central pipe of the cyclone. A return system provided with a conventional cyclone is thus very sensitive to the suction flows of the return pipe and requires an absolutely reliable gas lock. In steam boiler applications the use of a conventional cyclone leads to a disadvantageous structure, as the conventional cyclone divides the boiler into a separate combustion chamber and a convection part positioned after the cyclone, between which there is disposed equipment for returning the solid material.
Mechanical gas locks wear quickly, especially under hot conditions and they often suffer from operational disturbances.
It is also known to position a conventional cyclone inside a reactor, whereby the entire system for returning the solids is situated inside the reactor. The big disadvantages of this system are the corrosion and erosion problems of the cyclone, as the cooling of the supporting structure cannot be arranged by simple means. Moreover, the system suffers from the sensitivity of the conventional cyclone to the suction flows of the return pipe.